[37.20] Observation of CO2 fluorescent emission at the limb of Mars by OMEGA/Mars Express

Observations in limb geometry with the imaging spectrometer
OMEGA on board Mars Express (Bibring et al, Nature, 2004) at
4.3~\mum have been obtained at various longitudes and
solar zenith angle between January and July 2004. They
present prominent off-limb emission in CO2, which
correspond to fluorescent emission of solar light in non-LTE
regime. A peak emission is observed at ~90 km. Emission of
CO2 fundamental is observed as well as isotopic
13CO2. Spatial/spectral scans allow us to observe the
vertical structure of the atmosphere at a kilometric
vertical scale. CO fluorescence is also observed, and
vertically resolved, with peak altitude at ~50km. Variation
in intensity and in altitude of the peak emission is
observed from orbit to orbit, which seem to indicate
atmospheric variability in the upper atmosphere, possibly
related to atmospheric structure. Observations in limb
geometry will continue with Mars Express to cover other
latitude and longitude during the nominal mission. In
addition to CO and CO2 emission, O2 dayglow emission
is also detected in the Northern regions, with a strong
latitudinal variation.